Bringing this back because asset bundles will not do what I need it to.
I'd like to ask for spec and emission to be pickable maps for custom mesh objects. The reason is that the textures that I'm going to be using are generated server-side rather than uploaded to my server manually.

Can we remove the [Solved] Tag on this, because it is not actually solved.
The suggested feature is an illumination and spec map slot in the existing Custom Mesh object, just like Diffuse and Normal. While asset bundles would normally be a viable solution, unfortunately it is not possible as the desired textures are determined server-side.

Forum ate my reply..
Bump and can we, for the love of all that is divine, please remove the solved tag on this thread?
Asset bundles will not work and since there have been several dozen updates since this was originally suggested, it's getting overlooked.